- Location
- sandiego, ca.
trying to figure out if the superbore head bolts right on with the 951 domes and if it does what domes give what psi.
Super Jet ada head on group k bb850 yamaha
- Thread starter jduplease2002
- Start date
- Location
- sandiego, ca.
the first answer is the only answer he gives. I've been looking around and people have asked this question but i haven't found an answer. Called ada and they didn't know either.
Ok, what follows is speculation on my part, but somewhat educated speculation. The bore of that cylinder starts out at 88.50 mm. The ADA 951 domes are good for that bore, without a doubt.
I had an ADA stroker cylinder set up by Art Gomez (Jetworks) that was at 89.00 mm starting bore and it used the ADA superbore domes, which are for the Seadoo 951 pistons. That's exactly what I used, for what it is worth. I do not know what pistons Harry uses in his 845cc stock stroke.
With my 89.00 mm bore, my cranking compression was right at 185 psi. Here's the bad news: I do not recall what size those domes where. ADA lists 40cc - 52cc available. I am guessing I was at around 46-47cc, but I am not sure.
Here is a handy chart ADA has for dome volume correlating to compression ratio, but this is dependent on stroke, as well. My own motor was set up with a little bit of negative deck height that required my domes to be cut a bit, so please do not take my sizes as guideline for your own.
However, you should be able to calculate your own (uncorrected) compression ratios fairly easily. Harry may be able to point you towards an acceptable compression ratio if he isn't able or willing to help with the dome size itself.
Edit: Someone correct me if I am wrong, but uncorrected compression ratio is cylinder volume (not taking exhaust port duration into account) divided by dome volume.
At 88.50 bore and 68 mm stroke (stock stroke), you have 418.3 cc volume per cylinder.
So with a 46 cc dome, you would have an (uncorrected) compression ratio of 1:9.1
I had an ADA stroker cylinder set up by Art Gomez (Jetworks) that was at 89.00 mm starting bore and it used the ADA superbore domes, which are for the Seadoo 951 pistons. That's exactly what I used, for what it is worth. I do not know what pistons Harry uses in his 845cc stock stroke.
With my 89.00 mm bore, my cranking compression was right at 185 psi. Here's the bad news: I do not recall what size those domes where. ADA lists 40cc - 52cc available. I am guessing I was at around 46-47cc, but I am not sure.
Here is a handy chart ADA has for dome volume correlating to compression ratio, but this is dependent on stroke, as well. My own motor was set up with a little bit of negative deck height that required my domes to be cut a bit, so please do not take my sizes as guideline for your own.
However, you should be able to calculate your own (uncorrected) compression ratios fairly easily. Harry may be able to point you towards an acceptable compression ratio if he isn't able or willing to help with the dome size itself.
Edit: Someone correct me if I am wrong, but uncorrected compression ratio is cylinder volume (not taking exhaust port duration into account) divided by dome volume.
At 88.50 bore and 68 mm stroke (stock stroke), you have 418.3 cc volume per cylinder.
So with a 46 cc dome, you would have an (uncorrected) compression ratio of 1:9.1
Last edited:
- Location
- sandiego, ca.
thanks Matt for all the info and taking the time to write it up. I'll try again tomorrow and see what he says. I was hoping someone who has done this could chime in.
Freakrider
X247
- Location
- Tampa Bay area
My domes are 53.6 on a 62t with Blowsion superbore sleeves 855 with 89.5 mm CR500 pistons. Cranking compression is 210 and 93 octane safe thus far. Cylinder built by XS, these sleeves are definitely different than GroupK's custom order so your results will probably vary.
Nuklear6
I Dream 10' Surf!
I answer alot of technical questions on this board and I'm pretty sure I've never been more qualified to answer a question as this one. All my first super bore engines used group k pistons. I've had and measured the group k sleeves vs blowsions sleeves and they are almost identical. Actually I believe they are one and the same. That being said the Blowsion set up uses cr500 pistons which are .155" taller (top of wrist pin to top of piston) then stock Yamaha. This is why the Blowsion ss 850 needs a spacer plate even though the stroke and rod length is stock. Group k pistons are stock Yamaha height but have a almost flat top squish angle. I believe off the top of my head top piston angle if 4 degrees or less. All this being said a group k 845 cylinder with Ada super bore head and even the smallest 951 domes (38cc) will not only have compression below 155 but will also have a squish angle and squish ratio that is all wrong.
- Location
- sandiego, ca.
dam, well that answers that. thanks a lot for all the info